He witnessed me rubbing off the semen from the clothe of the Messenger of Allah ﷺ. Abu Dawud said: Al-A'mash narrated it as narrated by al-Hakam.  

أَنَّهُ كَانَ عِنْدَ عَائِشَةَ ؓ فَاحْتَلَمَ فَأَبْصَرَتْهُ جَارِيَةٌ لِعَائِشَةَ وَهُوَ يَغْسِلُ أَثَرَ الْجَنَابَةِ مِنْ ثَوْبِهِ أَوْ يَغْسِلُ ثَوْبَهُ فَأَخْبَرَتْ عَائِشَةَ فَقَالَتْ لَقَدْ رَأَيْتُنِي وَأَنَا أَفْرُكُهُ مِنْ ثَوْبِ رَسُولِ اللَّهِ ﷺ  

I used to rub off the semen from the clothe of the Messenger of Allah ﷺ. He would would pray in it. Abu Dawud said: Mughirah, Abu Ma'shar, and Wasil also narrated it to the same effect.  

كُنْتُ أَفْرُكُ الْمَنِيَّ مِنْ ثَوْبِ رَسُولِ اللَّهِ ﷺ فَيُصَلِّي فِيهِ  

I heard 'Aishah say that she would wash semen from the clothe of the Messenger of Allah ﷺ. She added: Then I would see a mark or marks (after washing).  

سَمِعْتُ عَائِشَةَ تَقُولُ إِنَّهَا كَانَتْ تَغْسِلُ الْمَنِيَّ مِنْ ثَوْبِ رَسُولِ اللَّهِ ﷺ قَالَتْ ثُمَّ أَرَى فِيهِ بُقْعَةً أَوْ بُقَعًا